The present invention relates to a system and method for incinerating waste materials. In particular, the invention relates to a system for incinerating waste materials at high temperatures and under high turbulence, thereby to increase the efficiency of the combustion process and to decrease fly ash emissions.
Environmental concerns have motivated a search for waste incineration systems capable of efficiently incinerating waste materials while decreasing emissions of pollutants. The need for such systems is especially critical in the disposal of high-moisture wastes such as wood pulp or sewage and in the disposal of hospital wastes which are often contaminated or infectious. Traditional incinerating systems which simply burn waste materials in a combustion chamber under relatively low turbulence and at relatively low temperatures tend to emit unacceptably high amounts of fly ash and other pollutants to the atmosphere. Such systems are particularly ill-suited for the incineration of contaminated or infectious waste materials or of materials having relatively high amounts of moisture. If these waste materials are to be incinerated, care must be taken to incinerate completely the waste, to minimize the emission of fly ash, and to dispose of the toxic residual ashes remaining from the combustion process. While several systems have been designed to maximize combustion by dividing the combustion chamber into at least two separate combustion chambers separated by a step in the refractory liner defining the chambers, these systems still tend to operate at unacceptably low temperatures and to emit excessive amounts of fly ash.
Although some attempts have been made to reduce the emissions of toxic pollutants, these systems have proved incapable of economically handling infectious or contaminated waste materials or materials having a high water content. For example, U.S. Pat. No. 4,940,006, which issued to S. Tamelli on July 10, 1990, discloses an incineration system which includes a combustion chamber which is throttled or stepped to define a combustion zone below the throttle point and an afterburning zone above the throttle point. Waste materials are introduced into the combustion zone from the side of the unit, and primary combustion air is introduced into the combustion chamber from below. Nozzles inject additional or secondary air at a high velocity into the unit at a location above the combustion zone. This secondary air forms a grid which prevents flue gasses from exiting the combustion zone without being intensely mixed with the secondary air. As a result, the flue gasses are retained in the combustion zone for a relatively long time where they are intensely mixed with the combustion air at relatively high temperatures. This results in improved incineration of waste materials, which in turn reduces fly ash emissions.
This system, while more efficient than previously known systems, is ill-suited for economically incinerating contaminated or infectious materials or materials having a high water content. Since primary and secondary air is cold-blown into the unit, considerable energy must be consumed to raise the temperatures of the burning materials to the preferred temperatures of 900.degree.-1050.degree. C., thus increasing the operating costs and reducing the efficiency of the system. Moreover, turbulence in parts of the combustion zone is reduced due to the manner in which the primary combustion air is drawn into the bottom of the unit. Although tertiary nozzles can be added to the combustion zone to reduce this problem, these nozzles increase the construction and operating costs of the system. In addition, this system lacks any device for ensuring the sterilization of residual ashes before their removal.